1. Field of the Invention
The present invention relates to a method and apparatus for controlling braking and stopping of the slewing of the upper slewing body which is slewingably provided on a construction machine.
2. Description of the Prior Art
It is important to satisfactorily brake and stop the slewing of the upper slewing body provided on a construction machine represented by a rotary crane. Conventionally, such a slewing stop action has been manually operated by a skilled operator, and therefore, there has been posed a great task to reduce a burden of the operator and secure a reliable safety.
Recently, there have been proposed various means for automatically braking and stopping the slewing of the above upper slewing body.
For example, Japanese Patent Laid Open No. Sho 62-13619 publication discloses an apparatus for detecting an angular inertia moment of an upper slewing body and controlling a slewing braking force on the basis of the detected result. Furthermore, Japanese Utility Model Laid Open No. Sho 61-197089 publication discloses an apparatus for calculating an inertia moment of a boom (upper slewing body) from various detection signals and performing the automatic control of a slewing stop on the basis of the calculated inertia moment and present slewing speed.
Both the above-mentioned conventional apparatuses merely pay attention to the inertia moment and deceleration of the whole upper slewing body to control the braking torque and effect the automatic stop. However, the hoisting load is oscillated in the oscillating direction with respect to the upper slewing body during the actual slewing braking, and movement of the slewing body is not always coincident with that of the hoisting load. Such an oscillation of the hoisting load results in pulling the upper slewing body during the slewing braking, whereby there occurs a difference between a theoretical deceleration and an actual deceleration, thus impairing accuracy of the slewing control. For example, in the case that there is attempted such a control as to completely stop the slewing in the state that the oscillation of the hoisting load does not finally remain, there possibly remains an oscillation of a hoisting load by an error caused by the oscillation of the load at the time of actual stop. Such an error of control becomes significant as the weight of the hoisting load increases.